The present invention relates to a method of making an Impatt diode and particularly to a method of making a high power Impatt diode suitable for millimeter wave applications.
Recently there has been much interest in developing electronic equipment which operates at millimeter wave-frequency. For use in this equipment, high power Impatt diodes have been developed which operate at these frequencies. Such diodes in general comprise a body of semiconductor material, such as silicon, having adjacent active regions of opposite conductivity types forming a PN junction therebetween, and a separate high conductivity region between each of the active regions and an adjacent surface of the body. Each of the high conductivity regions is of the same conductivity type as its adjacent active region. For operation at millimeter wave frequencies the active regions must be very thin, no greater than one micron. Also, to achieve efficient operation at a desired frequency, the conductivity of the various regions and the profile of the conductivity modifier therein must be accurately controlled.
One technique which has been used to make Impatt diodes is to start with a wafer of one conductivity type and diffuse into opposite surfaces of the wafer conductivity modifiers to form the various regions. Another technique which has been used is to epitaxially deposit in succession on a surface of a substrate various layers of the desired conductivity type with each layer forming one of the regions of the diode. The substrate is then removed by an etching technique. However, to form the regions having the narrow thickness and having the desired profiles of the conductivity modifiers required for operation at millimeter wave frequencies by either of these techniques is very difficult. Thus, these techniques are not suitable for commercial production of high power Impatt diodes which will operate at millimeter wave frequencies.